It is known in the art to reduce the running time of a broadcast program signal by removing segments of the signal from the program in a manner that minimizes the impact on the viewer. For example, an apparatus sold commercially under the name “the TIME MACHINE” is available from Prime Image, Inc. of San Jose, Calif., for accomplishing this result. The Time Machine is sold primarily for use in the television industry and is particularly suited to reducing the running time of audio-visual programs to create additional commercial time. The TIME MACHINE removes redundant video signal from a broadcast signal by identifying and removing video segments in which there is little or no relative motion. The TIME MACHINE also removes corresponding audio signal by identifying appropriate “splice points” in the audio signal while keeping the audio signal within an acceptable synchronization of the corresponding video signal.
While the video signal reduction techniques utilized in the TIME MACHINE are quite advanced, the audio signal reduction technique is relatively rudimentary. For example, while the audio component of a program may be in two or more channels, the TIME MACHINE reduces the audio signal by analyzing only one channel of the stereo signal. (Similarly, U.S. Pat. No. 4,463,784, titled “Pitch Change with Glitch Minimizer,” also analyzes only a single audio channel, and does not appear to even consider how to analyze and process multi-channel signals.) When the TIME MACHINE identifies signal suitable for removal in the one audio channel being analyzed, it removes corresponding material in the other audio channel with complete disregard for its audio content. This almost certainly would not be acceptable when the audio is contained in a large number of channels, such as in high-definition television (HDTV) which has six channel surround sound. Furthermore, even for the one audio channel that is analyzed, the algorithm employed by the TIME MACHINE for analyzing this channel is fairly static and cannot adapt to changing conditions in the audio signal.